The Dragon Plague was an ailment of unknown origin that spread rapidly among British Dragons throughout 1806 and 1807. The disease appeared to have be brought to Britain by a Dacota captured raiding British settlements in the Americas. The plague initially caused a loss of appetite and a lingering weakness or lethargy in an infected dragon. The tongue of an infected dragon became covered in a series of white blisters that hindered the individual's ability to taste. These symptoms become progressively worse and led to eventual death in all cases until a cure was found. Young and old dragons were found to be able to survive longest after infection, the disease was most swiftly fatal to middle-aged dragons.
A cure for the Dragon Plague was found entirely by accident by the Chinese chefs that accompanied Prince Yongxing on his return to China in 1806. During this voyage undertaken to determine the response to Temeraire's harnessing by William Laurence, Temeraire was infected by the Dragon Plague, though at the time it was only believed to be a normal sort of cold. In an attempt to reinvigorate Temeraire's appetite, during a stop at Cape Town, Laurence asked the chefs to prepare pungent dishes that would penetrate Temeraire's dulled senses. One of these dishes contained a particularly foul smelling mushroom, that was later shown to be able to counter the plauge.
In late 1807, with the mushroom that cured the plague established in growing caves in Scotland, the British admiralty undertook to infect as many continental dragons as possible with the plague to establish the British Ariel Corps superiority in Europe. This plan was undertaken by people who believed dragons were no more than beasts, and the intended consequence, the death of large numbers of intelligent dragons far from disturbing them was seen as a boon for the British Military position and a laudable goal. This view point was widely condemned by members of the British Ariel Corps, though their views were not given consideration by the Lords of the Admiralty, and indeed the entire Ariel Corps command structure was bypassed in the implementation of the scheme.